Yes, it is. But a relatively small increase in CO2 in the atmosphere will make the earth unlivable for HUMANS in a relatively short time.

For hundreds of millions of years before humans existed (or animal life at all) the earth's atmosphere was very rich in CO2 and the planet was covered with rich plant life. That's where all our fossil fuels came from. These plants breathed in CO2 and breathed out oxygen. Eventually there was so much oxygen that animals could survive, and we took over!

At this point, a relatively small increase in CO2 in our atmosphere will make it impossible for US to live, but easier for plants.

To a limited extent. Plants can only use so much carbon dioxide. But since too much carbon dioxide causes climate change, and perhaps warmer, wetter weather, this leads to plant diseases. Pathogenic fungi and insects often like such conditions.